1. Field of the Invention
The present invention relates to a scanning-type distance measuring apparatus for scanning a space to be measured with measurement light and measuring a distance to an object to be measured on the basis of the measurement light and reflection light from the object to be measured existing in the space to be measured.
2. Description of the Related Art
A scanning-type distance measuring apparatus of this kind is used in a navigation sensor as a visual recognition sensor for a robot or an unmanned vehicle, a door open/close sensor, a safety sensor for detecting a person or matter approaching a dangerous machine and safely stopping the machine, an ETC system sensor for detecting the shape of a car, determining the type of the car, and counting the number of cars passing, a traffic sensor for detecting people, counting the number of people, and detecting traffic and the flow of people, a monitor sensor for detecting the presence or absence of an intruder to a monitored area, and the like.
The scanning-type distance measuring apparatus has a light transmitting unit that outputs measurement light, a scanning unit that scans a space to be measured with the measurement light emitted from the light transmitting unit; a light receiving unit that detects reflection light from an object to be measured existing in the space to be measured; and a computing unit that calculates a distance to the object to be measured on the basis of the measurement light and the reflection light detected by the light receiving unit.
Such a scanning-type distance measuring apparatus is disclosed in U.S. Pat. No. 5,455,669 and Japanese Unexamined Patent Publication No. 2006-349449.
As shown in FIG. 13, a laser range finding apparatus 500 described in U.S. Pat. No. 5,455,669 has a light transmitting unit including a laser light source 504 and a lens 505, a light receiving unit including a light receiving lens 508 and a light receiving device 509 such as a photodiode, a transmission/reception mirror 503 attached to the rotation axis 501 of a motor 502, and a reflection mirror 506 that deflects measurement light from the light transmitting unit toward the transmission/reception mirror 503. Reflection light from an obstacle 507 in a space to be measured, in the measurement light deflected toward the space to be measured by the transmission/reception mirror 503, is deflected by the transmission/reception mirror 503 toward the light receiving unit. A horizontal plane is scanned with the measurement light by the rotation of the motor 502.
As shown in FIG. 14, a scanning-type distance measuring apparatus 200 described in Japanese Unexamined Patent Publication No. 2006-349449 includes: a light transmitting unit 201, a light receiving unit 202 disposed so as to oppose the light transmitting unit 201 on an optical axis P of measurement light output from the light transmitting unit 201; a cap member 204 driven to be rotated about the optical axis P by a motor 210; a light transmitting mirror 206 disposed on the top face of the upper wall of the cap member 204 at a predetermined tilt angle with respect to the optical axis P and deflecting the measurement light from the light transmitting unit 201 toward a direction perpendicular to the optical axis P; and a light receiving mirror 208 fixed on the under face of the upper wall of the cap member 204 at a predetermined tilt angle with respect to the optical axis P and deflecting reflection light from an obstacle R, in the measurement light output to a space to be measured, toward the light receiving unit 202.
In the laser range finding apparatus disclosed in U.S. Pat. No. 5,455,669, the single light transmission/reception mirror 503 serves as the deflecting mirror that deflects measurement light from the light transmitting unit toward the space to be measured and the deflecting mirror that deflects reflection light from the space to be measured to the light receiving unit, and reflection light having a large diameter is deflected toward the light receiving unit by a periphery part of the mirror. Consequently, the light transmission/reception mirror 503 needs to have a large deflecting face. Further, the light path of guiding reflection light to the light receiving unit is accordingly long, so that the diameter of the light receiving lens 508 is large. There is a problem of difficulty in miniaturization of the apparatus.
In the scanning-type distance measuring apparatus disclosed in Japanese Unexamined Patent Publication No. 2006-349449, the light transmitting mirror 206 and the light receiving mirror 208 are disposed close to each other via the upper wall of the cap member 204. Naturally, the distance between the optical axis of the measurement light deflected by the light transmitting mirror and that of the reflection light incident on the light receiving mirror is short. Consequently, the dead area in a close range can be reduced to the degree at which there is caused no problem in practical use. Further, since the light receiving lens 209 is provided on the light incidence side of the light receiving mirror in the cap member 204, the light receiving mirror can be made small, and the scanning-type distance measuring apparatus can be miniaturized.
However, the light transmitting mirror 206 and the light receiving mirror 208 are separated from each other by the cap member 204 and the light path of the measurement light and that of the reflection light are separated from each other. In a case where a light shield sheet or the like is made to adhere to a transparent window purposely or carelessly, the following problem occurs.
Even when measurement light output from the light transmitting unit 201 is reflected from the light shield sheet, the reflection light is not received by the light receiving unit, so that adhesion of the light shield sheet or the like cannot be detected. Consequently, when the scanning-type distance measuring apparatus is used in a monitor sensor or the like, the reliability cannot be assured.